Increased sensitivity to pressor hormones in central diabetes insipidus

Pressor sensitivities to infusions of arginine vasopressin (AVP), noradrenaline (NA) and angiotensin II (AII), as well as cardiovascular responses to head-up tilt, were assessed in subjects with central diabetes insipidus (CDI) and compared with those in normal control subjects. During incremental i.v. infusions of AVP at 0.2-5.0 pmol min-1 kg-1, mean arterial blood pressure (MABP) rose progressively in CDI subjects only and the rise was significantly greater than that which occurred in control subjects during their final infusion. The pressor effects of incremental i.v. infusions of NA and AII were greater, and the bradycardia associated with NA was more pronounced, in CDI subjects than in controls. Whole body tilt from supine to 45 degrees head-up was associated with increased heart rate and an insignificant rise in MABP in both groups, although a rise in plasma AVP occurred in control subjects only. These results demonstrate that subjects with CDI are more sensitive than control subjects to the pressor effects of NA and AII, and also develop sensitivity to the pressor effects of AVP. Their cardiovascular responses to head-up tilt remain intact. Presumably the increased vascular sensitivity to NA and AII in subjects with CDI is sufficient to compensate for their lack of AVP response during head-up tilt.